Field of the Invention
Embodiments of the present invention relate to a control apparatus for an internal combustion engine.
Description of the Related Art
Diesel combustion, in which fuel is directly injected into compressed air in the combustion chamber, self-ignites, and is burned by diffusion combustion, has a higher thermal efficiency as compared to combustion by spark ignition. In recent years, in order to enjoy this advantage of diesel combustion also in gasoline engines, technology for causing gasoline to self-ignite and burn by diffusion combustion has been developed.
For example, in the technology disclosed in Japanese Patent Application Laid-Open No. 2002-276442, first fuel injection is performed by an in-cylinder injection valve during the period in the first half of the compression stroke to produce substantially homogenous air-fuel mixture in the entirety of the combustion chamber. Then, the air-fuel mixture produced by the first fuel injection is spark-ignited. Thereafter, second fuel injection is performed to burn the injected fuel. With this combustion, the temperature and pressure in the combustion chamber rise to cause the remaining fuel to self-ignite.
Japanese Patent Application Laid-Open No. 2003-254105 discloses a technology enabling diesel combustion using as fuel natural gas or the like having a relatively high self-ignition temperature. According to Japanese Patent Application Laid-Open No. 2003-254105 disclosing this technology, fuel injection is performed in a predetermined spark-ignition region in the combustion chamber in an early or middle stage of the compression stroke to form an air-fuel mixture that can be spark-ignited. Then, the air-fuel mixture formed in the spark-ignition region is ignited at a time immediately before the top dead center of the compression stroke to bring about combustion by spark ignition. Thus, a high-temperature, high-pressure condition enabling self-ignition of natural gas is established in the combustion chamber. Thereafter, fuel is injected directly into the combustion chamber in a high-temperature, high-pressure condition, so that the injected fuel is burned by diesel combustion.